Not much is known about Mitsumushi, beyond that she is incredibly loyal to Seimei. One might even call her a familiar, depending on her origin. Knowing Seimei, Mitsumushi could have either been a butterfly given the power to change into a human, or a human given the power to change into a butterfly. Either way, she is to Seimei what Doson's Familiar is to Doson, and like Doson's Familiar the feelings go both ways, as Seimei more than cares about Mitsumushi. Furthermore, as long as she dies in her butterfly form, Seimei is able to resurrect Mitsumushi.